Magnetoresistive heads equipped with a magnetoresistive element (MR element) which acts as a magnetism sensing element have been used in dedicated playback heads that detect magnetic signals recorded on a magnetic recording medium such as a magnetic tape or a magnetic disk. An MR element is formed as a magnetoresistive film. Biasing layers, electrode layers, or the like are disposed at the edges of a side of the film. The electrical resistance of the magnetoresistive film changes in response to external magnetic fields.
The magnetoresistive head (hereinafter referred to as an MR head) is placed where a signal magnetic field from a magnetic recording medium is applied. A sensing current is supplied to the MR element, and potential changes in the MR element are detected. As a result, the magnetic signals recorded on the magnetic recording medium can be detected.
FIG. 4 illustrates a conventional magnetoresistive head 50. FIG. 4 is a detail drawing of the MR head 50 as seen from the plane facing the magnetic recording medium (the facing plane). A longitudinal bias layer 52 and an electrode layer 53 are disposed on either side of a centrally positioned MR element 51. Non-magnetic layers 54, a lower shield layer 55, and an upper shield layer 56 are disposed on either side of this structure.
As shown in FIG. 4, the MR element 51 includes a magnetoresistive film 51a (hereinafter referred to as MR film 51a), a transverse bias film 51b which applies a transverse bias magnetic field to the MR film 51a, and a magnetic separation film 51c which magnetically separates the MR film 51a and the transverse bias film 51b. These elements are formed at a predetermined width (track width) on the plane facing the magnetic recording medium. The pair of longitudinal bias films 52 at the ends of the MR element 51 apply a longitudinally biased magnetic field to the MR element 51.
In this MR head 50, the distance between the lower shield layer 55 and the upper shield layer 56 is the playback gap length. This playback gap length is a factor in determining the smallest magnetic signal that can be played back and, therefore, plays a significant role in playback characteristics.
The MR head 50 described above has been installed in hard drives as “flying heads” that do not make sliding contact with the magnetic recording medium during recording and playback. However, in recent years, MR heads are also being installed in tape-based recording/playback devices such as tape streamer devices.
In a tape streamer, the magnetic recording medium, in the form of a magnetic tape, slides at high speeds against the side of the MR head that faces the magnetic tape. This results in friction which can lead to problems. More specifically, if the MR head 50 slides against a magnetic tape, the metallic films forming the shield layers 55, 56, the longitudinal bias layer 52, and the electrode layer 53 wears or is dragged or moved. This can cause electrical or magnetic shorts in the elements making up the MR head 50. An electrical short circuit between the shield layers 55, 56 and the MR element 51 can cause the sensing current to become unstable, thereby deteriorating the quality of playback output. Such a sort circuit also prevents the biasing layer from applying an appropriate bias magnetic field to the MR film 51a. 